If you are SO SURE it's just the light, why don't you open the unit yourself and change the bulbs?
I've changed my fair share of bulbs in radio/audio/video equipment already. It's not really that hard and you can order replacement bulbs from mouser, digikey or even radioshack.
I'm sorry, but I do think that replacing the entire unit is a bit excessive. However, I do not think that the dealer has any choice. When it comes to electronics, the dealer changes entire units. That, unfortunately, is probably all that they are authorized to do.
The other alternative is to check out an electronics repair shop, if you can find one. It's not like you can void the warranty on your car anyway, and what's the worst that can happen - you'll have to replace the entire unit which you were probably going to do anyway.
